Prior art lighting domes, are known to those skilled in the art of photography. There are commercial domes for viewing semiconductor wafers that have a large hole in them for the lens to view through. For instance, a conventional dome reflector is typically a hollow hemispherical shell with a reflectively coated interior. Lights located along the interior rim of the shell reflect off the interior to illuminate an object to be viewed. For shiny spherical and convex objects, dome illuminations provide a somewhat diffuse and homogeneous light with less reflection.
Conventional optical systems use a lens with a front element whose size determines the aperture on the dome required to view the wafer. As this aperture size is increased the reflection of the lens in the image of the wafer makes a significant portion of the image unusable. To overcome this and other issues, U.S. Pat. No. 5,684,530 describes a second optical arrangement over the aperture in the dome to allow the illumination of the central spot with a second light source.
However, the disadvantages of this second optical arrangement include the following difficulties. The lighting in the central part through which the camera views the object is not truly multi-directional. The lighting for the central part is from a different light source so the colors and the intensities must be matched to that of the source for the dome making it difficult to use in practice. The height of the light source is increased. The beam-splitter through which the camera views the object can introduce changes to the light passing through it and obstruct the view of the object. What is needed is lighting dome technology that addresses the above-discussed issues in a cost-effective manner.
Meanwhile, the challenges of visual inspection or macro-inspection of semiconductor wafers include the following issues. The product can change from one batch to another, thereby changing the expectation of what a good wafer looks like. The product is highly reflective so it is difficult to illuminate without glares. A defect can be hard to define, especially when the failure mechanism is not known. These challenges make manual inspection of the wafers the industry default macro-inspection. But a disadvantage of this approach has been relatively high cost. What is needed is a wafer inspection solution that obviates the above-discussed issues in a cost-effective manner.